Hi Evan,

I, too, after Ian, doubt it's possible to accelerate text drawing on macOS by caching images.

But, FLTK 1.4 contains the code to get the proper alpha channel of antialiased text, because it's used

to draw text on GL scenes.

Use this virtual member function of class Fl_Gl_Window_Driver :

  virtual char *alpha_mask_for_string(const char *str, int n, int w, int h, Fl_Fontsize fs);

where

  str is the UTF8 text to draw, n is its length

  w, h is the size of the desired image containing the drawn text

  fs is the font size (the current font is used)

This function returns a char array of size w * h containing the adequate alpha channel for the text.

The effect of this function as antialiased text is visible with any text-drawing, GL-using FLTK program (e.g., test/cube).

The macOS implementation of this virtual function, Fl_Cocoa_Gl_Window_Driver::alpha_mask_for_string,

builds a CGContextRef for a CGBitmapContext which contains a depth-4 pre-multiplied byte array

that can also be used to create an adequate depth-4 Fl_RGB_Image object.